Numerous female couplers are currently available for coupling to and uncoupling from a pressurized or non-pressurized male coupler. Such couplers are used extensively in hydraulic hook-ups such as are used in agricultural and industrial vehicles. U.S. Pat. No. 4,303,098, entitled "Female Coupler" which issued on Dec. 1, 1981 to the assignee, describes such a coupler. In using a pair of the above-identified couplers, wherein one coupler serves to direct fluid from a pressurized supply source to one end of a hydraulic cylinder and the second coupler receives flow from the opposite end of the hydraulic cylinder and routes it to a sump, a problem occurs when fluid flow through the female couplers is intentionally blocked by closing a directional control valve associated with the second female coupler. Under these conditions, fluid flow into and out of the hydraulic cylinder is non-existent although the piston within the cylinder can fluctuate to a small extent. This fluctuation of the piston within the cylinder is caused by the implement, to which the cylinder is attached, being worked over uneven ground. As the piston fluctuates, the fluid on one side of the piston is compressed while the fluid on the opposite side of the piston experiences a pressure drop or vacuum. The pressure drop or vacuum is conveyed to the respective female coupler and results in a situation in which the fluid contained in the female coupler flows outward towards the hydraulic cylinder. This creates a vacuum within the main cavity. As this occurs, the main valve positioned in the female coupler may move and allow the male check ball to close upon a sudden surge of return oil from the hydraulic function. Once the male check ball is closed, a block is formed in the system which presents problems once the directional control valve(s) are again reopened. For example, as the directional control valves are reopened, pressurized fluid is allowed to pass through the first female coupler to the head end of the hydraulic cylinder. However, the piston within the cylinder will be unable to move because the fluid on the rod end of the piston will be blocked from flowing through the second female coupler due to the closed male check ball. Up until now, the only way the operator could correct this problem was to first reverse the flow thereby opening the male check ball associated with the rod end of the hydraulic cylinder and then again reversing the flow such that the flow would be directed to the head end of the hydraulic cylinder.
Now, a female coupler has been invented which overcomes this problem by using a flow check prevention mechanism to prevent the male check valve from closing should a vacuum occur in the second female coupler.